A display has an important role in an electronic device including imaging equipment and communication equipment, and with the increment of a user' desire for portability and conveniences and the development of flexible display panel technologies, a curved flexible display, which is bendable to a given degree, has been shipped. Further, a number of prior arts related to a rollable flexible display or foldable flexible display have been recently suggested.
In case of the existing prior arts, a motor or spiral spring is just used to generate a roller's driving force necessarily needed, with which a flexible display panel is rolled. In this case, it is hard to apply the motor to the flexible display because of the miniaturization trend of the flexible display and the limitation in the battery capacity, and it is also hard to apply the spiral spring to the flexible display because of the prescription function loss of the spiral spring, the difficulty in the occupation of space, and the problem of the control in rotational force. Up to now, however, there is no appropriate suggestion capable of solving the above-mentioned problems, and accordingly, there is a definite need for the development of a new method for generating the rotational force of the roller, not through the motor or spiral spring.